An antibody binds to a foreign substance such as a virus or bacterium, or an autoantigen such as cancer cells in a body, thereby playing a major role in the immune response for eliminating them from the body. Because of this, a method for artificially and efficiently inducing in vivo production of antibodies to these substances as targets of the antibody reaction can be significantly used as therapeutic and prophylactic methods against infectious diseases, cancers or the like. However, at present, a method for efficiently producing an antibody to any types of antigen has not yet been developed, thereby many infectious diseases, cancers or the like that cannot be treated are still present.
In order to produce a class-switched antibody in vivo by differentiating B cells into plasma cells, firstly an antigen must be recognized by T cells. In other words, an antibody of interest cannot be produced if the reaction with T cells does not occur. Since the reaction with T cells depends on an antigen recognition pattern of the T cell receptor, T cells do not react with an antigen which does not fit the pattern (called “T cell restriction”). For example, in cancer immunotherapy or the like, it is difficult to induce an antibody to a cancer antigen, which is not clearly distinguished from an autoantigen. This is because T cells having the T cell receptor recognizing a cancer antigen, which is a part of autoantigens, have been eliminated basically in the thymus and do not exist in the body. Although the possibility of recognizing an autoantigen by B cells slightly remains, without interaction with such autoreactive T cells, the B cells cannot be activated and do not produce the autoantibody. As such, a method of administering an adjuvant, as a substance which forces T cells to recognize an antigen and to overcome the T cell restriction, together with a cancer antigen is employed at present. However, even if this method is employed, drastic effects on antibody production against such an antigen which basically T cells do not recognize has not yet been obtained.
A vaccine against an infectious disease can be generated if an antigen of pathogen is fully prepared. However, unless a culture system for providing a pathogen in a large scale is established, such a vaccine cannot be developed. Particularly, a vaccine against an emerging pathogens which mass culture system is still unknown cannot be prepared with this method. It will also require many years to establish an appropriate culture system. In addition, even if the mass culture method for a pathogen is established, in the case that the pathogen frequently and quickly mutates, in other words, the pathogen has a so-called genetic polymorphism for its pathogenic antigen, it will take time to adapt culture system to the mutation of pathogen and it is also difficult to overtake polymorphism.
Considering those issues above, development of synthetic peptide vaccines has been extremely focused in recent years. Of them, a multiple antigen peptide (MAP) has particularly attracted attention. MAP can be obtained by using, for example, a conjugate, as a core, containing a plurality of lysine (Lys) residues and optionally containing cysteine (Cys) residue which are one of amino acids to bind a peptide (a part of the antigen to be well recognized by cells) to an a amino group and an c amino group of Lys or to a sulfhydryl group of Cys.
For example, a MAP is used against Diplococcus pneumoniae in Patent Literature 1. Specifically, the literature describes that two sites are selected from an antigen peptide of Diplococcus pneumoniae and the two peptides are alternately arranged to form a MAP4 structure having four peptides in total.
Patent Literature 2 describes a multiple antigen peptide that has a T cell epitope bound therein and is capable of inducing both a humoral immune response and a cytotoxic T lymphocyte immune response.
Non-Patent Literature 1 describes as follows: a B cell epitope (a peptide region easily recognized by the B cell receptor or a membrane-bound antibody on the B cell surface) in antigen group B of Neisseria meningitidis and a T cell epitope (a peptide region recognized by T cell) were generated as synthetic peptides, both of which were combined to form a MAP. The MAP was administered concomitantly with an adjuvant to mice and rabbits and then an increase of the antibody titer was examined. As a result, the antibody titer did not increase in a MAP (MAP-8) obtained by binding eight same B cell epitopes; whereas, the antibody titer increased in a MAP (MAP-4) consisting of two identical B cell epitopes and two identical T cell epitopes.
Non-Patent Literature 2 describes that a MAP having a T cell epitope(s) for malaria parasite bound therein and a MAP having a T cell epitope(s) and a B cell epitope(s) in combination were generated inducing an antibody against the B cell epitope.
Non-Patent Literature 3 describes as follows: a MAP (MAP-4) having 4 same B cell epitopes for an anthrax antigen bound therein was used concomitantly with a Freund's adjuvant. To examine antibody production by the MAP, a rabbit model was selected, which was capable to forcibly recognize the epitope as a T cell epitope with the adjuvant. As a result, a neutralization antibody titer increased in the rabbits. In a mouse model, since the epitope was considered as a hapten or non-T cell epitope of mice, antibody production with the MAP was not expected.
In these findings of the prior arts, there is a common recognition that a MAP should be recognized by T cells to induce antibody against the MAP on the condition that T cell recognition of a peptide is inevitable to induce antibody production.